Thanks guys, I have tried a few things such as adopting a dubious pose behind the vehicle with a hand behind each exhaust but needless to say it won't do it then! Plugs leads coil etc seem OK - maybe the injector cleaning stuff will help but this isn't typical from my experience. It has occurred in similar fashion for about 450 miles - I would expect some further deterioration. The ECU switch with the other car is next on the list. The right hand pot on car No.1 has always had the sound of an exhaust valve leaking but it never gets worse so I agree with the fluffy running on that side but this is not the same on the problem car. I'll persevere and keep you up to date.
Phil
